Coal preparation process and magnetite reclaimer for use therein

ABSTRACT

A coal preparation process includes a dense medium coal separator which utilizes a magnetite media for separating raw coal from refuse. A sieve receives coal from the separator and is utilized to drain a portion of the magnetite media from the coal before the coal is passed into a new magnetite reclaimer wherein paddles agitate the coal causing abrasive contact between the coal particles to dislodge the magnetite which adheres to the coal. The magnetite free coal is conveyed out of the reclaimer by a screw conveyor while the released magnetite is removed by a magnetic drum. The magnetite removed from the coal is directed into a sump for re-use in the system. A similar process is utilized to treat the refuse so as to recover the magnetite which passes from the separator with the refuse.

United States Patent [191 Burkitt 1 June 5, 1973 [54] COAL PREPARATIONPROCESS AND MAGNETITE RECLAIMER FOR USE THEREIN [75] Inventor: ShermanC. Burkitt, Arlington Heights, 111.

2,690,262 9/1954 Bean ..209/l72 5 2,753,998 7/1956 Mardinge 209/172 52,949,190 8/1960 Pagnotti 209/172 5 2,964,184 12/1960 Gillette......209/225 X 3,247,961 4/1966 Chase ..209/172.5 X

OTHER PUBLICATIONS Link-Belt, 100D Catalog, pps. 403-411 PrimaryExaminer-Frank W. Lutter Assistant Examiner-Robert Halper Attorney-F. W.Anderson and C. E. Tripp [52] US. Cl. ..209/10, 209/40, 2O9/l72.5,

209/223, 209/232, 209/464 57 ABSTRACT [51] Int. Cl. ..B03b 7/00, B03c1/30 h 58 Field of Search .209/10, 214, 232, A Preparatm! a l ""P209024426, 209 39, 1725 223, 40, 472 coal separator WhlCh utilizes amagnetite media for 3 464 separating raw coal from refuse. A sievereceives coal from the separator and is utilized to drain a portion of[56] References Cited the magnetite media from thermal before the coalis passed into a new magnetite reclaimer wherein pad- UNITED STATESPATENTS dles agitate the coal causing abrasive contact between the coalparticles to dislodge the magnetite which adgl f heres to the coal Themagnetite free coal is conveyed 946:394 [1910 out of the reclaimer by ascrew conveyor while the 1,153,037 9/1915 Davis "209/232 releasedmagnetite is removed by a magnetic drum. 1,340,457 5/1920 Newton D209/40 The magnetite removed from the coal is directed into 1,392,41310/1921 (3 w 309 232 a sump for re-use in the system. A similar processis 1,475,394 11/1923 Jordanm. ..209/40 utilized to treat the refuse soas to recover the mag- 2,002,978 5/1935 Davis netite which passes fromthe separator with the refuse. 2,216,371 10/1940 Leveke ..209/464 X2,325,149 7/1943 Rakowsky ..209/l72.5 X 21 Claims, 14 Drawing Figures 7RAW souos RECLAIMER Z65 CIRCULATI NG SUMP T0 CLARIFICATION Patented June5, 1973 9 Sheets-Sheet 4 CLEAN COAL TO CLARIFICATION TO CLARIFQCATIONPatented June 5, 1973 3,737,032

9 Sheets-Sheet 6 Patented Jun 5, 1973 9 Sheets-Sheet '7 Patented June 5,1973 9 Sheets-Sheet 9 BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates generally to a process of preparingcoal but more particularly relates to a process of reclaiming magnetitefrom coal or other solids which have been processed in a magnetic densemedium system. An important feature of the invention is a magnetitereclaimer for abrasively releasing the magnetite from the solids andseparating the two materials for individual processing.

The use of heavy media, that is to say a suspension of finely dividedhigh gravity solids such as magnetite in water or other liquids, for thebeneficiation of coal by a sink and float process has achieved greatcommercial utility. In a sink and float process, raw coal is fed into adense medium separator wherein the medium has a specific gravity whichis greater than that of the coal but less than that of the refuse whichis to be separated from the coal. There are numerous types of suchseparators but each functions similarly in that the raw coal is placedin contact with the dense medium so that the refuse, which isintermingled with the coal, sinks into the medium and is, therefore,called the sink product while the coal floats on the medium surface andis consequently called the float product. The coal can then be removedseparately from the refuse. The coal, of necessity, however, entrains acertain quantity of the magnetite which must be removed from the coal ifthe coal is to be thoroughly cleaned. In addition, and more importantly,the recovery of the magnetite, which can be re-used in the process, isnecessary for an efficient and economical operation.

The present invention is accordingly concerned with a system forseparating float and sink products with a dense magnetite medium andwith a system which removes and recovers the magnetite from theseparated float and sink products with a new magnetite reclaimingapparatus.

2. Description of the Prior Art In conventional coal preparationprocesses, each product discharged from the separating device isrelieved of its magnetite coating by passing the product over adewatering sieve and finally over a vibrating rinsing screen beforeremoving the product from the system. While passing over the vibratingscreen the material is rinsed with a liquid medium in an attempt toremove the adhering magnetite from the solids. The rinse medium,magnetite, and ultra fine non-magnetic solids are collected in a panbelow the screen. To recover the magnetite from this solution, thesolution is processed through a recovery system which may includevarious combinations of magnetic separators, cyclones, staticthickeners, densifiers and storage tanks.

The conventional processes are not entirely satisfactory, however, as ithas been found that the magnetite clings to the coal and is notadequately removed by a mere rinsing. This is particularly true in thepreparation of smaller coal particles wherein there is a greater surfacearea of coal exposed to the magnetite media per unit weight of coal.

Typical of prior art devices used for removing magnetic particles fromtheir carrying medium are disclosed in US. Pat. No. 2,002,978 issued toE.W. Davis on May 28, 1935 and U.S. Pat. No. 2,564,5 l5 issued to W.Vogel on Aug. 14, 1951. U.S. Pat. No. 2,998,882 issued to J.M.J. Leemanon Sept. 5, 1961 discloses a process and apparatus for purifying asuspension of fine magnetizable particles in a liquid solutioncontaining contaminated particles of a non-magnetizable material.

SUMMARY OF THE INVENTION The process of the present invention providesan efficient and effective system for the recovery of magnetic materialfrom solids which have been processed in a magnetic dense medium system.A new magnetite reclaimer, which is part of the coal preparation system,makes it possible to omit in most installations the vibrating screenwhich is critical to the successful operation of conventional systems.

In general, raw coal is fed into a dense medium separator which utilizesthe specific gravity of the medium to separate refuse from the coal. Inother words a dense magnetic solution having a predetermined specificgravity peculiar to the separator type is passed through the separatorwith the coal. The coal being lighter than the refuse will be separatedfrom the heavier refuse particles and consequently each will beseparately carried out of the separator through different passages by afraction of the solution. Inherently, a certain quantity of the magneticsolution will adhere to and be carried from the separator by bothproducts. The float and sink products emanating from the separator aretreated in a similar manner to remove the magnetic material from thesurfaces thereof so that the magnetic material can be re-used in thedense medium separator.

For purposes of the present disclosure, the magnetic material will bereferred to as magnetite, however, other magnetic type solids may beused.

It has been found by applicant that a scrubbing action of one particleon another has the ability to very effectively free the adheringmagnetite from the particles. When this is done in a fluid pool withagitation, the magnetite is free to move through the liquid medium fromwhich it can be removed by magnetic means. To treat the coal and refuseparticles in this manner, applicant has developed a magnetite reclaimerfor use in the coal preparation process.

The magnetite reclaimer contains a liquid bath and has means foragitating the magnetite laden particles to cause a scrubbing actionbetween the particles to release the magnetite. The reclaimer is alsoprovided with means for removing the released magnetite from the bath,means for removing the particles which formerly carried the magnetite,and means for removing nonmagnetic fine particles which are unavoidablycarried into the system by the raw coal.

Accordingly, it is an object of the present invention to provide a densemedium coal preparation process wherein a very efficient and effectiverecovery of the magnetite used in the dense medium can be made.

It is another object to provide an apparatus for removing magnetite fromsolids being processed and separately discharging the separatedproducts.

It is still another object to provide an apparatus for removingmagnetite from solids to which the magnetite is adhered by abrasivelyagitating the solids to thereby scrub the magnetite from the surface ofthe solids.

It is still another object to provide an apparatus for removingmagnetite from solids to which the magnetite is adhered by abrasivelyagitating the solids to thereby scrub the magnetite from the surfaces ofthe solids then collecting the magnetite by magnetic means anddischarging the magnetite separately from the cleansed solids.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic representation of thecoal preparation process.

FIG. 1A is a schematic representation of an alternative embodiment ofthe process of FIG. 1.

FIG. 1B is a schematic representation of another alternative embodimentof the process of FIG. 1.

FIGS. 1C and ID are fragmentary schematic representations of furtheralternative embodiments of the process of FIG. 1.

FIG. 1E is a schematic representation of still another alternativeembodiment of the process of FIG. 1.

FIG. 2 is a diagrammatic isometric view of a portion of the apparatusused in the process schematically shown in FIG. 1.

FIG. 3 is a diagrammatic isometric view of a portion of the apparatusused in an alternative arrangement of the process schematically shown inFIG. 1.

FIG. 4 is a diagrammatic front elevation of the magnetic drum separatorused in an alternative arrangement of the process schematically shown inFIG. 1.

FIG. 5 is a side elevation of a preferred embodiment of the magnetitereclaimer of the present invention with parts broken away for clarity.

FIG. 6 is an enlarged sectional view of the magnetite reclaimer of FIG.5 taken along line 66 of FIG. 5.

FIG. 7 is an enlarged fragmentary view of the magnetite reclaimer ofFIG. 5 showing the magnetite discharge chute.

FIG. 8 is a longitudinal vertical section of an alternative embodimentof the magnetite reclaimer.

FIG. 9 is a sectional view of the alternative embodiment of themagnetite reclaimer of FIG. 8 taken along line 99 of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An understanding of the coaltreating process of the present invention is best understood byreference to FIG. 1 wherein a schematic representation of one embodimentof the process is shown. It is seen that raw solids consisting of coaland refuse such as gravel, etc., are fed into a dense medium separatorwherein the coal is conventionally separated from the heavier refuse.The dense medium of the separator is comprised of magnetite and waterconstituting a magnetite slurry. The refuse or sink product is carriedfrom the separator 20 with the magnetite slurry while the coal or thefloat product is removed separately. However, due to the manner in whichthe separator operates, a certain quantity of the magnetite slurryadheres to and is carried from the separator by the coal. The emittedfloat and sink products are subsequently similarly treated to recoverthe magnetite carried thereby for re-use in the system.

The float and the sink products are treated with identical equipment intwo separate branches B and B of the system. The coal or float productbranch B includes a drying apparatus not generally included in the sinkor refuse branch B but otherwise the systems are identical.

The coal. and refuse products from the separator 20 are firstrespectively passed over identical dewatering sieves 22 and 22 whereinmost of the slurry is drained from the solid coal or refuse. Theslurries leaving the sieves are directed through flow lines 25,. and 25respectively into a circulating medium sump 24 for reuse in theseparator while the coal and refuse are respectively passed intoidentical magnetite reclaimers 26;- and 26 through passages 27 F and 27The magnetite reclaimer is an important feature of the invention, aswill be seen hereinafter, and includes means for agitating the solidsfor abrasively releasing the magnetite from the surfaces thereof. Thereleased magnetite is removed from the reclaimers by magnetic means anddirected into the circulating medium sump 24 through flow lines 29 and29 The clean coal is removed from the magnetite reclaimer 26 in branch Bby mechanical means through a solid particle discharge passage 33 andpassed into a centrifugal dryer 28 wherefrom the coal is emitted as aclean and de-watered product. The moisture removed from the coal in thedryer 28 is directed into a liquid sump 30 through flow line 31 fromwhich it is pumped back for use in the reclaimer in either the coalbranch or the refuse branch of the system.

The clean refuse is mechanically removed from the magnetite reclaimer 26in the refuse branch B; but is generally not passed through a dryer asthere is usually no need to further process the refuse. Once emittedfrom the reclaimer, the refuse can be carried away from the system by aconveyor or any other suitable means.

The circulating medium sump 24 is provided with a regulated water supply32 and a fresh magnetite supply 34 so that the specific gravity of themagnetite slurry in the sump 24 can be maintained at a predeterminedvalue. The water supply 32 is regulated by conventional means includinga density meter 35 in a flow line 36 from the sump 24 to the separator20, level indicators 38 disposed in the sump 24, and a gravity controlinstrument 40 for operating a solenoid valve 42 in a water line 43. Thefresh magnetite supply 34 is regulate manually or automatically asdesired.

The magnetite slurry in the sump 24 is pumped by a pump 44 through line36 to an inletof the separator 20 to thereby recirculate the magnetitewhich was separated from the coal and refuse particles in thepreparation system. A bleed-off line 46 is provided in the flow line 36to divert slurry from the flow line 36 to help maintain the desiredspecific gravity of the magnetite slurry. The bleed-off line 46 is alsouseful to further purify the slurry by re-directing a portion of theslurry through the magnetite reclaimers 26p and 26 wherein the finenon-magnetic particles, which got into the circulating sump andconsequently the flow line 36 through the sieves 22p and 22 can beremoved by a process to be described in more detail hereinafter.

The bleed-off line 46 is provided with a deflector valve 48 toselectively direct the flow of liquid in line 46 into one or both of twore-cycling lines 49 and 50. The re-cycling line 49 is connected to theinlet of the magnetite reclaimers 26p and 26g and re-recycling line 50is directed back into the circulating medium sump 24. It has been foundin some installations that fine non-magnetic particles will pass throughthe sieves 22p and 22 with the magnetite slurry and tend to undesirablyincrease the specific gravity and/or viscosity of the media in the sump24. Therefore, to prevent this increase in specific gravity, the fluidpassing in the bleedoff line 46 can be primarily deflected intore-cycling line 49 leading back into the reclaimers 26 and 26 whereinthe non-magnetic particles can be separated from the magnetite anddirected through an overflow line 52 to clarification or otherprocessing systems not comprising a part of the present invention, andthe magnetite can be fed back into the sump 24. Thus, it is apparentthat the bleed-off line 46 provides a means of ridding the system ofundesirable non-magnetic fine particles and also provides an additionalmeans for regulating the specific gravity of the media in the sump 24completely independent of the water supply 32 or the fresh magnetitesupply 34.

A portion of the apparatus used in the processing of the coal or floatproduct is diagrammatically shown in FIG. 2, it being understood thatthe apparatus used in the processing of the refuse is identical exceptthat normally there is no apparatus provided in the refuse ranch fordrying the solid particles. The separator is disclosed as being of thevessel type used for fine or intermediate size coal, preferably in therange between onefourth inch to 28 mesh, but may be used on coal up toinches. The separator, may be similar to the Wilmot OCC heavy mediaseparator, which consists of a straight walled cylinder 56 (FIG. 2) ofpredetermined length and diameter, provided at each end with a head 58and 60. The cylinder is operated in an inclined position. The raw solidfeed enters the vessel through a feed pipe 62, while the magnetiteslurry enters the unit tangentially under pressure through a pipe 64 atthe lower end of the cylinder 56. The pipe 64 is in fluid communicationwith flow line 36. The pumped slurry rises to the top of the vesselcreating an open longitudinal vortex 66 (FIG. 2). The slurry leaves thevessel through a refuse discharge pipe 68, and through a float dischargepipe 70. The actual separation takes place on the inner face of thevortex 66 in such a manner that the light float coal rides downwardly tobe discharged as clean coal through the float discharge pipe 70 whilethe heavy refuse particles of feed penetrate the rising magnetite slurrytoward the outer wall of the vessel and are discharged with the highgravity slurry through the refuse discharge pipe 68.

As stated hereinbefore, upon leaving the separator 20 the coal (or floatproduct) passes into a branch B of the preparation system while therefuse (or sink product) passes into the similar branch B With furtherreference to FIG. 2, it is seen that the sieve 22p which receives thecoal leaving the separator through discharge pipe 70, includes aninclined screen 72 having a mesh so that the magnetite slurry and otherfine non-magnetic particles can pass therethrough but through which thelarger coal particles cannot pass. The magnetic slurry and non-magneticfines leave the sieve 22,. through a conduit 74 which is in fluidcommunication via flow line 25,. with the circulating medium sump 24.The coal which is still moist with the magnetite slurry, and to someextent the non-magnetic fines, is passed into the magnetite reclaimer26,. through inlet conduit 76.

The magnetite reclaimer will be described in more detail later, however,it is important to note at this point that the reclaimer veryefiiciently separates the magnetite, coal, and non-magnetic fines intothree distinct discharged products. The magnetite is passed through aflow line 29; (FIG. 1) directly into the circulating medium sump 24, thenon-magnetic fines are passed through the overflow line 52 toclarification or other processing systems, and the coal is passed in amoist state into the centrifugal dryer 28.

One type of centrifugal dryer can also be seen in FIG. 2, and comprisesa feed chute made of two frustoconical members to first funnel the coaland then disperse it onto the bottom surface of a screen-walled tub 82.The tub 82 is rotated through a belt-pulley drive 84 by a motor 86. Thescreen wall of the tub is outwardly flared and is non-symmetricallyweighted so that centrifugal force and vibratory action will cause thecoal particles to rise up and over the top of the wall and into astationary annular solids discharge passage 88 wherefrom they flow bygravitational force out of the bottom of the dryer. As the coal isrising up the flared screen wall of the tube 82, the moisture on thecoal is centrifugally forced through the screen wall into an annularliquid discharge passage 90 wherefrom it flows out of the dryer throughopening 91 which communicates with the flow line 31 (FIG. 1) going tothe liquid sump 30.

The above described coal preparation process may be varied to meetvarious requirements determined by the installation size or the qualityof the raw coal to be processed in the system. Various alterations areshown in FIGS. 1A through 1E. One variation (FIG. 1A) can be seen to beadding identical vibrating screens 94 and 94 into the system between thesieves 22 and 22 and the magnetite reclaimers 26 and 26 3 respectively.This vibrating screen can be used in either or both branches B and B ifit is found that the sieves 22,- and 22 are not adequately removing asubstantial quantity of the magnetite slurry. The screen would merelyprovide an additional means for draining the slurry from the solids.

One type of vibrating screen which could be used in the system is showndiagrammatically in FIG. 3, wherein branch B of the system is depicted,and can be seen to include a horizontally disposed screen 96 rigidlysecured in a resiliently mounted frame member 98. A vibrator 100 issecured to the frame at an acute angle to the screen so that the screenis vibrated in a manner so as to throw the solid particles passingthereover forwardly in small increments. The moisture carried by theparticles is thereby shaken from the particles as the particles advanceover the screen causing the moisture to fall through the screen into adischarge pan 101 from where it is directed into the circulating sump 24via flow line 102p- Of course, the vibrating screen 94; in branch Bwould operate the same way with the moisture falling through the screenbeing passed through flow line 102 Another variation in the coalpreparation process (FIG. 113) would be the addition of a conventionalmagnetic drum separator 104. The drum separator can be incorporated intothe system to aid in recovering any magnetite escaping the reclaimer inthe overflow water. The magnetic drum separator is useful in separatingthe magnetite that is carried in liquid suspension from other liquidsuspendable material such as nonmagnetic fines. One type of separatorconsists of a metallic cylindrical drum member 106 (FIG. 4) rotatablydriven in the direction of arrow 107 with the lowermost portion of thedrum submerged in a liquid medium. A stationary arcuate magnet 108 isdisposed within and adjacent the solid cylindrical drum wall 109 of thedrum 106, so that the magnetic field of the magnet is always effectiveon the portion of the drum wall passing through the liquid medium toattract magnetic material suspended in the liquid medium to the outersurface of the drum. The magnet 108 extends arcuately a finite distanceabove the liquid medium level on the upwardly moving side of the drum todefine a magnetic material discharge position at its uppermost extent.The outer surface of the drum wall carries the magnetic material out ofthe liquid and to the magnetic material discharge position. As the drumwall rotates past the magnetic material discharge position the magneticmaterial on the drum wall leaves the magnetic field of the magnet 108and falls therefrom into a discharge chute 110. The chute 110communicates with a flow line 111 which directs the magnetic materialinto the circulating medium sump 24 for. re-use in the system.

A liquid feed passage 1 12 is provided on the opposite side of the drumfrom the magnetic discharge chute 110 having a filtering screen 114therein to prevent the entry of oversize tramp material. The liquidpasses from the feed 1112 into the main tank 116 wherein the magneticmaterial is picked up by the drum 106. A tailing discharge 118 isprovided to remove the nonmagnetic solids from the tank along with agood portion of the liquid,and an overflow liquid discharge 120 isprovided to maintain an effective operating level. Both discharges 118and 120 are directed into a common duct 122 and the combined flow passesinto the overflow line 52 for removal from the system.

The drum separator 104 can be incorporated into the system to receive.the overflow from the magnetite reclaimers 26 and 26 The drum would inthis case be used as a check to remove any magnetite from the reclaimeroverflows that was not removed in the reclaimers. The drum can also beused to receive the liquid medium flowing in recycling line 49 in lieuof directing the flow in line 49 into the reclaimers, inasmuch as thesame result would be achieved, namely separation of the magneticparticles from the liquid, and as a consequence thereof an overload onthe reclaimers could be avoided. The vibrating screens 94; and 94 couldalso be incorporated into the system of FIGS. 13 just as they wereincorporated into the system of FIG. 1A.

Another variation (FIG. 1C) in the preparation process is to direct theliquid effluent from the dryer 28 directly into the overflow line 52 andthus out of the system rather than directing the effluent into the sump30 and subsequently to the feed chute of the reclaimers as in the firstdescribed arrangement of the system. This variation would be useful whenit was evident that the magnetite was sufficiently separated from thewetting liquid in the reclaimer 26 and there was no need to feed theliquid back into either or both of the reclaimers for furtherseparation. To provide better control over the liquid flow from thedryer to the overflow line 52, the effluent liquid from the dryer couldbe directed into sump 30 (FIG. 1D), as in the first describedarrangement of the system, wherein it can be collected and pumped asdesired into the overflow line 52. It should also be noted that thevibrating screens 94 and 94, and/or the drum separator 104 could also beadded to the systems of FIGS. 1C and/or 2D.

Still another variation (FIG. 1E) from the basic process describedhereinbefore would be to use the liquid in sump 30 as a water source viaflow lines 123 and 125 to maintain the liquid baths in the reclaimers ineither or both branches B and B of the system which will be more clearlyunderstood with the detailed description of the reclaimers which followshereinafter. Again it should be noted that the system variations shownin FIG. 1A (vibrating screens 9% and 9%) and/or FIG. 1B (magnetic drumseparator 104) could also be incorporated into the system of FIG. 1E.

As mentioned before, an important feature of the present invention isthe magnetite reclaimer. The description of the reclaimer will be madewith reference to the reclaimer 26 shown in detail in FIGS. to 7,

' it being understood that the reclaimer 26 in the branch B isidentical, differing possibly in size in some installations. Thereclaimer 26 can be seen to include an elongated and inclined liquidbath retaining tank 124 having a lower agitating section 126 and anupper screw conveyor section 128.

Extending longitudinally through the tank 124 are two parallel andinclined shafts 130 and 131 (FIG. 6) rotatably driven in oppositedirections by a motor and drive unit 132. It is of course possible thatmore than two shafts could be used without altering the overall functionof the machine. The lower portion of the shafts in the agitating section126 of the tank is provided with a plurality of paddles 134 rigidlymounted on each of the shafts in a helical configuration. The upperportion of each of the shafts in the conveyor section 128 of the tank isprovided with an helical plate screw blade 138. The paddle and platescrew blade helixes on shaft 130 are left-handed while the paddle andplate screw blade helixes on shaft 131 are right-handed so that when theshafts are counter-rotated, material in operative contact with any oneof the helixes will be conveyed in the same direction.

Disposed vertically above the shafts 130 and 131 in the agitatingsection of the tank is a magnetic drum separator having a stainlesssteel cylindrical drum wall 142. The drum wall has substantiallyenclosed ends and is rotatably driven in the direction of arrow 141 by amotor 144. It is not critical that the drum wall be made of stainlesssteel, however, it is desirable that the drum wall be made of anon-magnetic material that will not deteriorate rapidly with constantexposure to the liquid medium in the tank. A stationary elongated magnet146 of arcuate cross section is mounted adjacent the interior surface ofthe drum wall so that the magnetic field of the magnet is alwayseffective on the portion of the drum wall passing through the liquidmedium of the bath to attract magnetic particles suspended in the liquidmedium to the outer surface of the drum. The magnet extends arcuately afinite distance above the liquid bath level on the upwardly turning sideof the drum wall to define a magnetic material discharge position at itsuppermost extent.

The tank 124' is provided with a water supply 148, the inlet or feedpassage 76 for magnetite laden solid particles which are to be cleanedin the reclaimer, and three discharge passages 33, 153 and 154 forremoving the separated products from the reclaimer. The water supply 148may consist of a trough 155 which extends across the entire width of thetank near the upper end and is provided with water through water pipe157. The pipe 157 is connected to a suitable water source (not shown).However, the trough 155 could be supplied with liquid from the sump 30via flow line 123 as was pointed out hereinbefore with regard to thealternative arrangement of the coal preparation system in FIG. 1E.

The discharge passage 33 is for removal of the heavier solid particleswhich have been relieved of substantially all of the magnetite whichthey carried into the reclaimer, discharge passage 153 is for removal ofthe magnetite which is separated from the solid particles in thereclaimer, and discharge passage 154 is an overflow passage to removewater and suspended nonmagnetic solids from the tank.

The overflow discharge passage 154 and the water supply 148 determinethe liquid level in the tank. This level is maintained so that a lowerportion of the drum separator 140 is submerged in the liquid.

In operation, solid magnetite bearing particles are fed into theagitating section of the reclaimer through feed passage 76 and have atendency to settle to the bottom. The rotating paddles 134 on the shafts130 and 131 serve to agitate the particles causing a scrubbing action ofone particle on another thus dislodging magnetite which is carried bythe particles. It is important to note that shaft 130 rotatescounterclockwise while shaft 131 rotates clockwise as viewed in FIG. 6,thus throwing the solid particles into abrasive contact in a regionbetween the respective shafts. This scrubbing action is particularlybeneficial in the treatment of fine solids as opposed to larger solidsinasmuch as there is a greater surface area per unit weight of materialfor the magnetite to 'occupy and consequently more magnetite to beremoved.

As the solids are agitated and the magnetite scrubbed from the surfaceof the solids, the magnetite and ultrifine non-magnetic material becomesuspended in the liquid of the tank because of the turbulence created bythe agitating paddles 134. The magnetic particles are drawn against theouter surface of the magnetic drum wall 142 and thereby withdrawn fromthe liquid bath as that portion of the drum wall is rotated out of theliquid. As can be seen in FIG. 6, the upper-most extent or longitudinaledge of the permanent magnet 146 which defines the magnetic materialdischarge position is disposed opposite the magnetite discharge passage153 so that as the magnetite held against the drum wall passes thisposition the magnetic attraction is lost and the magnetite will fallfrom the drum wall into the passage 153. To assure complete removal ofall the magnetite from the drum wall, a water manifold 156 may beprovided adjacent the discharge passage 153 with a plurality of spraynozzles 158 distributed along its length to wash the magnetite from thedrum wall. The manifold is connected to a water supply which is notshown. The opposite longitudinal edge of the magnet 146 extends a slightdistance beyond the overflow discharge passage 154 so that any magneticmaterial approaching the overflow discharge 154 will be drawn againstthe drum wall and will thus be prevented from passing over an overflowweir 160 and into the overflow passage 154.

Along with agitating the solid particles in the reclaimer, the paddles134, due to their helical arrangement, also convey the material up theinclined bottom wall of the tank to the screw conveyor section 128.Therein the plate screws 138 on the shafts 130 and 131 serve to transferthe material up through and out of the liquid in the tank and through adewatering area 161 before subsequently depositing the material into thesolid particle discharge passage 33. I

It should be noted that the water supply 148 is situated near the upperend of the inclined tank so as to induce a water flow toward therecovery area of the reclaim magnet 146. Magnetite scrubbed from thesolids in the agitating section 126 of the tank and which becomessuspended in the liquid bath will thus be urged by the water currents toremain in the recovery area thus assuring more complete recovery of theremoved magnetite. Also the fresh water pumped into the tank throughwater supply 148 serves to rinse the solids as they are being conveyedup the incline of the tank by the plate screw conveyor 138. Once emergedfrom the rinse water, the solids are conveyed by the screw conveyorthrough the dewatering section 161 to relieve the solids of all but athin moisture coating before they are discharged out passage 33.

The reclaimer of the present invention is designed to maintain aconstant liquid level for efficient operation of the magnetic drumseparator 140. In conventional magnetic separators, the majority of thefeed medium is discharged from the bath through fixed orifices in thebottom of the tank and a small portion overflows a weir in an attempt tomaintain a fixed bath level. This bath level is extremely important tothe performance of the separator. Loss of the bath can cause the loss ofmost of the magnetite contained in the separator feed. Inasmuch as thebath underflow orifices are fixed, any reduction in medium flow to theseparator such as might be caused by a plugged rinsing water line or areduction in rinse water pressure, can cause loss of the separatorliquid and consequent loss of large quantities of magnetite. In thereclaimer of the present invention, there are no underflow orifices andall liquid leaving the unit, must overflow the weir arranged to bringall magnetic particles into the magnetic field of the permanent magnet146. I

It will be appreciated from the description of the magnetite reclaimerthat an apparatus is provided that will efficiently and effectivelyseparate adhering magnetite from the surface of solid particles andrecover the magnetite for re-use in the coal preparation process. Thesolid particles are, as a consequence, cleaned and prepared forcommercial use.

An alternate embodiment of the magnetite reclaimer is shown in FIGS. 8and 9 and is designated 164. The reclaimer 164 is seen to include a tankhaving an outer cylindrical shell 166 with inlet and discharge end wallscomprised of generally frusto-conical housings 168 and 169 respectively,so that a liquid bath medium can be retained in the tank. The inlethousing 168 is provided with a central opening 170 through which a feedchute 172 can be inserted to pass magnetite laden solids into thereclaimer, and the discharge housing 169 is provided with a centralopening 174 through which the solids can be removed from the reclaimerin a manner to be described hereinafter.

The shell 166 has two exteriorly disposed annular tracks 176 which restupon supporting rollers 178. A ring sprocket 180 also circumscribes theexterior of the shell and meshes with a drive chain 182 which is drivenby a motor-sprocket unit 184 so that the shell can be continuouslyrotated about a horizontal axis.

The inner surface of the cylindrical-shell 166 has a plurality oflifters 185 affixed thereto to tumble the solids in the liquid bath. Thelifters are wedge-shaped and disposed in a helical pattern so as toadvance the solids through the reclaimer as the shell is rotated. Thetumbling solid particles are thus abrasively thrown against each othercausing a scrubbing action which releases the adhered magnetite from thesurface of the particles. The frusto-conical housing 169 of the shellhas affixed on its inner surface a plurality of angularly disposedlifting discharge shelves 186 that pick-up, as the reclaimer rotates,the solid particles which have been relieved of the adhering magnetiteand dump the particles through the opening 174 into a solids dischargechute 188. The chute 188 constitutes a sieve having a screen 189 throughwhich liquids will drain but through which the solids cannot pass. Thesolids slide off the screen and pass through a conduit 191 while thedrained liquid falls into a passage 193.

' Connected to the shell 166 and internally concentric therewith is acylindrical drum 190. The drum 190 is linked to the shell 166 by spokes192 at the inlet end of the reclaimer so that material fed into thereclaimer can pass through openings 187 between the spokes. At thedischarge end of the reclaimer, the drum 190 is rotatably supported by anon-rotatable shaft 194 passing through a bushing 195 in the center ofthe drum end 196. The shaft 194 is supported externally of the shell bya support block 197 on an externally supported I- beam 198. The drum190, is therefore, mounted to rotate with the reclaimer shell and islarge enough in diameter so that its lowermost portion at any given timeis submerged in the liquid bath.

An arcuate magnet 200 is disposed within the drum 190 and is fixed tolie adjacent the lowermost submerged portion of the drum as the drumrotates, thereby establishing a magnetic field through the cylindricaldrum wall to attract magnetic particles in the liquid bath against theouter surface of the wall. The uppermost extent of the arcuate magnet200 on the upwardly turning side of the drum is above the liquid bathlevel in the reclaimer and defines a magnetite discharge position 201 atwhich the magnetite falls from the drum wall into an adjacent inclinedmagnetite removal chute 202.

The inclined magnetite removal chute 202 projects into the reclaimerfrom the discharge end between the drum 190 and the shell 166. It isdisposed immediately adjacent the cylindrical drum wall on the upwardlyrotating side of the drum at the magnetite discharge position so that asthe particles pass the end of the magnet and lose their attraction tothe outer surface of the drum wall, they will fall into the removalchute. A water manifold 204 having spaced spray nozzles 206 extendsalong the entire length of the chute to fluidize the magnetite fallinginto the chute so that it will flow freely down the incline of the chuteand out of the reclaimer.

It is readily seen that this embodiment of the reclaimer will veryeffectively separate by agitation the solid feed particles from theadhering magnetite so that the magnetite may be recovered in aconcentrated solution for re-use in the coal preparation process. Toincorporate the reclaimer 164 into either or both branches of thehereinbefore described process, the feed chute 172 would be connected tothe flow line 27 or 27 emanating from the sieve 22 or 22 respectively sothat magnetite laden solids leaving the sieve would be fed into thereclaimer. The magnetite removal chute 202 would be connected to-theflow line 29 of branch 8;, or the flow line 29 of branch B leading intothe circulating medium sump 24. The solids discharge conduit 191 wouldbe aligned in branch B with the feed chute 80 of the dryer 2%, or inbranch B with a discharge line from the system. The drained liquidpassage 193 would in either branch be connected to overflow line 52 forpassage to clarification or other processing systems not comprising apart of the present invention.

Although the best mode contemplated for carrying out the presentinvention has been herein shown and described, it will be apparent thatmodification and variation may be made without departing from what isregarded to be the subject matter of the invention.

' What I claim is:

1. Apparatus for separating finely sized high gravity magnetic materialfrom a liquid medium having nonmagnetic solids carrying the magneticmaterial on their surface, and ultra-fine non-magnetic particles,comprising in combination:

a. a tank structure for maintaining a liquid bath having an inclinedbottom wall establishing an upper and lower end of the tank, said tankhaving a feed inlet passage at the lower end for admitting the liquidmedium a discharge outlet passage for the nonmagnetic solids at theupper end, a liquid supply adjacent the upper end of said tank, and anoverflow weir adjacent the lower end of said tank, whereby a constantflow of liquid can be maintained through the tank and the ultra-finenonmagnetic particles which are carried into the tank with the saidnon-magnetic solids and which become suspended in the liquid bath can beremoved from the tank over the overflow weir;

b. agitating means in the tank for abrasively agitating the non-magneticsolids in the liquid bath, said agitating means including at least twocounterrotating shafts parallel to the inclined bottom wall of the tank,each shaft having a lower section with a plurality of agitating paddlesmounted in a helical configuration followed by a helical plate screwblade, said paddles and said screw blade on one shaft being of oppositehand to those on the other shaft so the material in contact with saidpaddles and said screw blade will be conveyed in the same directiontoward the discharge outlet for the nonmagnetic solids, the counterrotation of said agitating paddles mixing and throwing the solids intoabrasive scrubbing contact with each other in a region between therespective shafts to thereby dislodge the finely sized magnetic materialfrom the surface of the solids; and

c. a magnetic drum separator rotatably mounted about a horizontal axisand positioned vertically above the agitating paddles in the lower endof the tank with the longitudinal axis of said drum separator parallelto the longitudinal axis of said counterrotating shafts of saidagitating means, said drum separator having a non-magnetic cylindricalwall extending below the surface of the liquid bath into the regionabove and between the counter-rotating agitating paddles, said drumseparator further having an elongated magnet of arcuate cross sectionstationarily mounted adjacent the interior surface of said drum wall sothe magnetic field of the magnet is effective on the portion of the drumwall passing through the liquid bath to thereby attract the freedmagnetic particles suspended in the agitated liquid medium to the outersurface of the drum.

2. The apparatus of claim 1 wherein said over-flow weir is located onone longitudinal side of the lower end of the tank structure and saidmagnetic drum separator is disposed parallel to and closely adjacentsaid overflow weir to define a relatively narrow channel through whichthe liquid and suspended ultra-fine nonmagnetic particles pass to saidoverflow weir, one longitudinal edge of the magnet in said magnetic drumseparator extending arcuately a slight distance above said overflow weirand projecting over the narrow channel to the overflow weir.

3. The apparatus of claim 2 wherein the drum wall of said magnetic drumseparator rotates oppositely to the flow of the liquid and suspendedultra-fine nonmagnetic particles in said narrow channel passing to saidoverflow weir, said drum wall being partially submerged in the liquidbath, whereby the counterflow motion of the drum wall in the liquid bathin the narrow channel tends to agitate the liquid to further separateany magnetic material from the ultra-fine particles so the magneticmaterial will be attracted by the magnet to the drum wall and therebyprevent the magnetic material from passing over the overflow weir.

4. The apparatus of claim 3, wherein the other longitudinal edge of themagnet of said magnetic drum separator extends arcuately a finitedistance above the level of the liquid bath on the upwardly turning sideof the drum wall of the magnetic drum separator to define a magneticmaterial discharge position at its uppermost extent, the magneticmaterial falling off said drum wall beyond said uppermost extent of saidmagnet as the magnetic attraction is lost, the magnetic material thenbeing collected in a magnetic material discharge passage extendinglongitudinally parallel to said drum wall and located below saiduppermost extent of said magnet, but above the liquid bath level, saidmagnetic material discharge passage thus being located on the oppositeside of said magnetic drum separator from said overflow weir to furtherminimize the magnetic material remixing and being discharged over theoverflow weir with the liquid and ultra-fine particles.

5. The apparatus of claim 4, further including a liquid spray at saidmagnetic material discharge position to wash the magnetic material offthe outer surface of the drum wall into said magnetic material dischargepassage.

6. The apparatus of claim 1, wherein said tank structure furtherincludes a dewatering area through which the solid particles aretransferred by said helical plate screw blades subsequent to leaving theliquid bath, but prior to being discharged through said solid particledischarge passage, said liquid supply further serving to rinse the solidparticles in the dewatering area to release any remaining magneticmaterial and ultra-fine particles and serving to induce a counter flow,opposite to the flow of the solid particles, of the released magneticmaterial and ultra-fine particles into the lower agitated section of theliquid bath where the magnetic material may be separated and recoveredby the magnetic drum separator and the ultra-fine particles may flow outover the overflow weir.

7. An apparatus for separating finely sized high gravity magneticmaterial from a liquid medium having non-magnetic solids carryingmagnetic material on their surface and having ultra-fine non-magneticparticles and for removing the magnetic material from the apparatusseparately from the solids and the ultra-fine particles, comprising incombination:

a. an outer cylindrical shell having frusto-conical end housings and aninner concentric cylindrical drum connected to said outer shell arrangedso that a liquid bath can be retained in the shell, one end housinghaving a central feed inlet opening and the other end housing having acentral discharge opening, said inner drum having a wall portionextending below the surface of the liquid bath;

b. means for rotating said shell about a substantially horizontal axis;

0. a plurality of lifters disposed in a helical pattern and attached tothe inner surface of said shell, said lifters lifting and tumbling thesolids in the liquid bath as the shell is rotated so the solids arethrown against each' other in an abrasive scrubbing action to releasethe magnetic material from the surface of the solids and to suspend themagnetic particles in the liquid bath, said helical pattern of saidlifters advancing the solids toward said discharge opening; and

d. an elongated magnet of arcuate cross section stationarily mountedadjacent the interior wall portion of said inner drum so the magneticfield of said magnet is effective on the portion of the drum wallpassing through the liquid bath to thereby attract the freed magneticmaterial, suspended in the agitated liquid medium, to the outer surfaceof said rotating inner drum, the uppermost extent of said arcuate magneton the upwardly turning side defining a discharge position for themagnetic material.

8. The apparatus of claim 7 further including a stationary dischargechute for the separated magnetic material projecting longitudinally intothe interior of said outer shell and located between the outer shell andsaid inner drum on the upwardly turning side of the drum,

said discharge chute further located adjacent the drum wall and slightlybelow said discharge position for the magnetic material so that as themagnetic material passes the upper end of the magnet and loses itsattraction to the outer surface of the drum wall the magnetic materialfalls into the discharge chute, said discharge chute for the magneticmaterial providing for the removal of the magnetic material through saidcentral discharge opening separately from the non-magnetic solids, theultra-fine particles and the liquid.

9. The apparatus of claim 8 further including a water manifold havingspaced sprays extending longitudinally along said discharge chute forthe magnetic material to insure that the magnetic material will flow inthis discharge chute and pass out of the apparatus.

10. The apparatus of claim 8 further including a discharge hopperstationarily supported outside said rotating shell and positioned toreceive the separated nonmagnetic solids, the ultra-fine particles andthe liquid discharging from said central discharge opening separatelyfrom the magnetic material, said discharge hopper including a screensection permitting the ultra-fine particles and the liquid to passthrough the screen section into a collection passage and said screensection retaining the non-magnetic solids so they pass off over the endof the screen section into a separate conduit.

11. The apparatus of claim 10 further including a feed chutestationarily supported outside of said rotating shell and positioned toproject into said central feed inlet opening so as to feed the liquidmedium into the liquid bath inside of said rotating shell.

12. A coal preparation process for treating fine or intermediate sizeraw coal in a dense medium type of separator using a finely sized highgravity magnetic material in a liquid to establish the dense medium of aparticular specific gravity required to separate the coal d. feeding theoversize solids of the coal and refuse fractions from the separate fixedsieves into separate magnetic material reclaimers;

e. agitating the oversize solids in a liquid bath within the separatereclaimers to throw the solids into abrasive scrubbing contact with eachother to' dislodge the magnetic material from the surface of the solidsand to put the freed magnetic material into suspension in the liquidbath;

f. magnetically attracting the magnetic material in suspension to a wallsurface of a rotary drum of each reclaimer partially submerged in theliquid bath through the action of a magnetic field of a stationaryarcuate magnet suspended inside the rotary drum;

g. collecting the separated magnetic material dropping from the rotarydrum surface after the magnetic material passes out of the liquid bathand beyond the upper end of the magnet;

h. conducting the collected magnetic material from the magnetic materialreclaimers to the magnetic material slurry sump;

recirculating the magnetic material slurry in the sump to the densemedium separator vessel for separating the raw coal; and j. dischargingthe coal from the coal fraction and the refuse from the refuse fractionfrom the bath in their respective magnetic material reclaimers free ofany magnetic material.

13. The process of claim 12 further including the step of controllablyadding makeup water and fresh magnetic material to the magnetic materialslurry sump to maintain the specific gravity of the magnetic materialslurry in the sump at a predetermined value.

14. The process of claim 12 further including the step of removingmoisture from the wet coal discharged from the coal fraction magneticmaterial reclaimer.

15. The process of claim 14 further including the step of utilizingcentrifugal force to extract the moisture from the wet coal.

16. The process of claim 14 further including the step of recirculatingthe moisture removed from the coal to.

the magnetic material reclaimers.

17. The process of claim 12 further including the step of bleeding-olf aportion of the recirculated magnetic material slurry to maintain thedesired specific gravity in the medium of the dense medium separatorvessel.

18. The process of claim 17 further including the step of removingultra-fine non-magnetic particles, which pass into the magnetic materialslurry sump with the undersize from the sieves, from the bled-offportion of the recirculated magnetic slurry by passing the bled-offportion to the magnetic material reclaimers and by discharging theultra-fine non-magnetic particles with the liquid from the overflowweirs of the magnetic material reclaimers.

19. The process of claim 12 further including the step of passing thecoal from the coal fraction sieve over a de-watering vibrating screen toremove an additional quantity of the finely sized magnetic material andliquid before feeding the oversize coal solids to the coal fractionmagnetic material reclaimer and conducting this additional quantity ofmagnetic material and liquid to the magnetic material slurry sump.

20. The process of claim 12 further including thestep of passing therefuse from the refuse fraction sieve over a de-watering vibratingscreen to remove an additional quantity of the finely sized magneticmaterial and liquid before feeding the oversize refuse solids to therefuse fraction magnetic material reclaimer and conducting thisadditional quantity of magnetic material and liquid to the magneticmaterial slurry sump.

21. The process of claim 12 further including the step of passing theoverflow from both coal and refuse fraction magnetic material reclaimersthrough a magnetic separator to remove any magnetic material escaping inthe overflow liquid, conducting the separated magnetic material to themagnetic material slurry sump and discharging the balance of the liquidfrom the magnetic separator.

3 3 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,737,032 Dated JUNE 5, 1973 Iriventor(x) SHERMAN c; BURKIT'I' It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

{- Column 5, line 23: before "inches" insert -1 l/2--. 1

Signed and sealed this 4th day of February 1975.

(SEAL) Attest: I I

MCCQY 1:4. GIBSON JR. C. MARSHALL DANN Attestmg Officer Commissioner ofPatents

1. Apparatus for separating finely sized high gravity magnetic materialfrom a liquid medium having non-magnetic solids carrying the magneticmaterial on their surface, and ultra-fine nonmagnetic particles,comprising in combination: a. a tank structure for maintaining a liquidbath having an inclined bottom wall establishing an upper and lower endof the tank, said tank having a feed inlet passage at the lower end foradmitting the liquid medium a discharge outlet passage for thenon-magnetic solids at the upper end, a liquid supply adjacent the upperend of said tank, and an overflow weir adjacent the lower end of saidtank, whereby a constant flow of liquid can be maintained through thetank and the ultra-fine non-magnetic particles which are carried intothe tank with the said non-magnetic solids and which become suspended inthe liquid bath can be removed from the tank over the overflow weir; b.agitating means in the tank for abrasively agitating the nonmagneticsolids in the liquid bath, said agitating means including at least twocounter-rotating shafts parallel to the inclined bottom wall of thetank, each shaft having a lower section with a plurality of agitatingpaddles mounted in a helical configuration followed by a helical platescrew blade, said paddles and said screw blade on one shaft being ofopposite hand to those on the other shaft so the material in contactwith said paddles and said screw blade will be conveyed in the samedirection toward the discharge outlet for the nonmagnetic solids, thecounter rotation of said agitating paddles mixing and throwing thesolids into abrasive scrubbing contact with each other in a regionbetween the respective shafts to thereby dislodge the finely sizedmagnetic material from the surface of the solids; and c. a magnetic drumseparator rotatably mounted about a horizontal axis and positionedvertically above the agitating paddles in the lower end of the tank withthe longitudinal axis of said drum separator parallel to thelongitudinal axis of said counter-rotating shafts of said agitatingmeans, said drum separator having a non-magnetic cylindrical wallextending below the surface of the liquid bath into the region above andbetween the counter-rotating agitating paddles, said drum separatorfurther having an elongated magnet of arcuate cross section stationarilymounted adjacent the interior surface of said drum wall so the magneticfield of the magnet is effective on the portion of the drum wall passingthrough the liquid bath to thereby attract the freed magnetic particlessuspended in the agitated liquid medium to the outer surface of thedrum.
 2. The apparatus of claim 1 wherein said over-flow weir is locatedon one longitudinal side of the lower end of the tank structure and saidmagnetic drum separator is disposed parallel to and closely adjacentsaid overflow weir to define a Relatively narrow channel through whichthe liquid and suspended ultra-fine non-magnetic particles pass to saidoverflow weir, one longitudinal edge of the magnet in said magnetic drumseparator extending arcuately a slight distance above said overflow weirand projecting over the narrow channel to the overflow weir.
 3. Theapparatus of claim 2 wherein the drum wall of said magnetic drumseparator rotates oppositely to the flow of the liquid and suspendedultra-fine non-magnetic particles in said narrow channel passing to saidoverflow weir, said drum wall being partially submerged in the liquidbath, whereby the counterflow motion of the drum wall in the liquid bathin the narrow channel tends to agitate the liquid to further separateany magnetic material from the ultra-fine particles so the magneticmaterial will be attracted by the magnet to the drum wall and therebyprevent the magnetic material from passing over the overflow weir. 4.The apparatus of claim 3, wherein the other longitudinal edge of themagnet of said magnetic drum separator extends arcuately a finitedistance above the level of the liquid bath on the upwardly turning sideof the drum wall of the magnetic drum separator to define a magneticmaterial discharge position at its uppermost extent, the magneticmaterial falling off said drum wall beyond said uppermost extent of saidmagnet as the magnetic attraction is lost, the magnetic material thenbeing collected in a magnetic material discharge passage extendinglongitudinally parallel to said drum wall and located below saiduppermost extent of said magnet, but above the liquid bath level, saidmagnetic material discharge passage thus being located on the oppositeside of said magnetic drum separator from said overflow weir to furtherminimize the magnetic material remixing and being discharged over theoverflow weir with the liquid and ultra-fine particles.
 5. The apparatusof claim 4, further including a liquid spray at said magnetic materialdischarge position to wash the magnetic material off the outer surfaceof the drum wall into said magnetic material discharge passage.
 6. Theapparatus of claim 1, wherein said tank structure further includes adewatering area through which the solid particles are transferred bysaid helical plate screw blades subsequent to leaving the liquid bath,but prior to being discharged through said solid particle dischargepassage, said liquid supply further serving to rinse the solid particlesin the dewatering area to release any remaining magnetic material andultra-fine particles and serving to induce a counter flow, opposite tothe flow of the solid particles, of the released magnetic material andultra-fine particles into the lower agitated section of the liquid bathwhere the magnetic material may be separated and recovered by themagnetic drum separator and the ultra-fine particles may flow out overthe overflow weir.
 7. An apparatus for separating finely sized highgravity magnetic material from a liquid medium having non-magneticsolids carrying magnetic material on their surface and having ultra-finenon-magnetic particles and for removing the magnetic material from theapparatus separately from the solids and the ultra-fine particles,comprising in combination: a. an outer cylindrical shell havingfrusto-conical end housings and an inner concentric cylindrical drumconnected to said outer shell arranged so that a liquid bath can beretained in the shell, one end housing having a central feed inletopening and the other end housing having a central discharge opening,said inner drum having a wall portion extending below the surface of theliquid bath; b. means for rotating said shell about a substantiallyhorizontal axis; c. a plurality of lifters disposed in a helical patternand attached to the inner surface of said shell, said lifters liftingand tumbling the solids in the liquid bath as the shell is rotated sothe solids are thrown against each other in an abrasive scrubbing actionto release the magnetic material from the surface of the solids and tosuspend the magnetic particles in the liquid bath, said helical patternof said lifters advancing the solids toward said discharge opening; andd. an elongated magnet of arcuate cross section stationarily mountedadjacent the interior wall portion of said inner drum so the magneticfield of said magnet is effective on the portion of the drum wallpassing through the liquid bath to thereby attract the freed magneticmaterial, suspended in the agitated liquid medium, to the outer surfaceof said rotating inner drum, the uppermost extent of said arcuate magneton the upwardly turning side defining a discharge position for themagnetic material.
 8. The apparatus of claim 7 further including astationary discharge chute for the separated magnetic materialprojecting longitudinally into the interior of said outer shell andlocated between the outer shell and said inner drum on the upwardlyturning side of the drum, said discharge chute further located adjacentthe drum wall and slightly below said discharge position for themagnetic material so that as the magnetic material passes the upper endof the magnet and loses its attraction to the outer surface of the drumwall the magnetic material falls into the discharge chute, saiddischarge chute for the magnetic material providing for the removal ofthe magnetic material through said central discharge opening separatelyfrom the non-magnetic solids, the ultra-fine particles and the liquid.9. The apparatus of claim 8 further including a water manifold havingspaced sprays extending longitudinally along said discharge chute forthe magnetic material to insure that the magnetic material will flow inthis discharge chute and pass out of the apparatus.
 10. The apparatus ofclaim 8 further including a discharge hopper stationarily supportedoutside said rotating shell and positioned to receive the separatednon-magnetic solids, the ultra-fine particles and the liquid dischargingfrom said central discharge opening separately from the magneticmaterial, said discharge hopper including a screen section permittingthe ultra-fine particles and the liquid to pass through the screensection into a collection passage and said screen section retaining thenon-magnetic solids so they pass off over the end of the screen sectioninto a separate conduit.
 11. The apparatus of claim 10 further includinga feed chute stationarily supported outside of said rotating shell andpositioned to project into said central feed inlet opening so as to feedthe liquid medium into the liquid bath inside of said rotating shell.12. A coal preparation process for treating fine or intermediate sizeraw coal in a dense medium type of separator using a finely sized highgravity magnetic material in a liquid to establish the dense medium of aparticular specific gravity required to separate the coal from therefuse and for recovering the magnetic material, comprising the stepsof: a. passing the raw coal through a dense medium separator vessel toseparate the raw coal into a coal fraction and a refuse fraction, eachfraction having some adhering magnetic material from the dense medium onthe surface of the solids in each fraction; b. passing both coal andrefuse fractions over separate fixed sieves; c. collecting the undersizeof the coal and refuse fractions and liquid from the separate fixedsieves in a magnetic material slurry sump; d. feeding the oversizesolids of the coal and refuse fractions from the separate fixed sievesinto separate magnetic material reclaimers; e. agitating the oversizesolids in a liquid bath within the separate reclaimers to throw thesolids into abrasive scrubbing contact with each other to dislodge themagnetic material from the surface of the solids and to put the freedmagnetic material into suspension in the liquid bath; f. magneticallyattracting the magnetic material in suspension to a wall surface of arotary drum of each rEclaimer partially submerged in the liquid baththrough the action of a magnetic field of a stationary arcuate magnetsuspended inside the rotary drum; g. collecting the separated magneticmaterial dropping from the rotary drum surface after the magneticmaterial passes out of the liquid bath and beyond the upper end of themagnet; h. conducting the collected magnetic material from the magneticmaterial reclaimers to the magnetic material slurry sump; i.recirculating the magnetic material slurry in the sump to the densemedium separator vessel for separating the raw coal; and j. dischargingthe coal from the coal fraction and the refuse from the refuse fractionfrom the bath in their respective magnetic material reclaimers free ofany magnetic material.
 13. The process of claim 12 further including thestep of controllably adding makeup water and fresh magnetic material tothe magnetic material slurry sump to maintain the specific gravity ofthe magnetic material slurry in the sump at a predetermined value. 14.The process of claim 12 further including the step of removing moisturefrom the wet coal discharged from the coal fraction magnetic materialreclaimer.
 15. The process of claim 14 further including the step ofutilizing centrifugal force to extract the moisture from the wet coal.16. The process of claim 14 further including the step of recirculatingthe moisture removed from the coal to the magnetic material reclaimers.17. The process of claim 12 further including the step of bleeding-off aportion of the recirculated magnetic material slurry to maintain thedesired specific gravity in the medium of the dense medium separatorvessel.
 18. The process of claim 17 further including the step ofremoving ultra-fine non-magnetic particles, which pass into the magneticmaterial slurry sump with the undersize from the sieves, from thebled-off portion of the recirculated magnetic slurry by passing thebled-off portion to the magnetic material reclaimers and by dischargingthe ultra-fine non-magnetic particles with the liquid from the overflowweirs of the magnetic material reclaimers.
 19. The process of claim 12further including the step of passing the coal from the coal fractionsieve over a de-watering vibrating screen to remove an additionalquantity of the finely sized magnetic material and liquid before feedingthe oversize coal solids to the coal fraction magnetic materialreclaimer and conducting this additional quantity of magnetic materialand liquid to the magnetic material slurry sump.
 20. The process ofclaim 12 further including the step of passing the refuse from therefuse fraction sieve over a de-watering vibrating screen to remove anadditional quantity of the finely sized magnetic material and liquidbefore feeding the oversize refuse solids to the refuse fractionmagnetic material reclaimer and conducting this additional quantity ofmagnetic material and liquid to the magnetic material slurry sump. 21.The process of claim 12 further including the step of passing theoverflow from both coal and refuse fraction magnetic material reclaimersthrough a magnetic separator to remove any magnetic material escaping inthe overflow liquid, conducting the separated magnetic material to themagnetic material slurry sump and discharging the balance of the liquidfrom the magnetic separator.